SURFACE ENHANCED INFRARED SPECTROSCOPY

Transcription

1 SURFACE ENHANCED INFRARED SPECTROSCOPY A. Pucci 1), F. Neubrech 2), J. Bochterle 1),S. Wetzel 1), C. Huck 1), S. Wetzel 1), J. Vogt 1), R. Wolke 1) 1) Kirchhoff-Institute für Physik, Universität Heidelberg 2) 4. Physikalisches Institut, Universität Stuttgart

2 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 2 IR vibrational sensing, example Blue phosphorescent emitter material CN CH, CH 3 mer-ir(cn-pmbic) nm 4.5 nm at 55 at 80 on Au 22.5 nm Relative reflectance spectra (IRRAS, p- plorized light) of mer-ir(cn-pmbic) 3 taken during growth on a gold substrate at room temperature. Thickness is increasing in steps of about 3.6 nm from top (0.9 nm) to bottom (22.5 nm). on Si 150 nm Transmittance spectrum for a thicker layer (150 nm) on silicon at room temperature. T. Glaser, et al., physica status solidi (a) 208, 1873 (2011)

3 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 3 IR vibrational sensing, example Blue phosphorescent emitter material CN CH, CH 3 mer-ir(cn-pmbic) nm 4.5 nm at 55 at 80 on Au 22.5 nm Relative reflectance spectra (IRRAS, p- plorized light) of mer-ir(cn-pmbic) 3 taken during growth on a gold substrate at room temperature. Thickness is increasing in steps of about 3.6 nm from top (0.9 nm) to bottom (22.5 nm). on Si 150 nm Transmittance spectrum for a thicker layer (150 nm) on silicon at room temperature. T. Glaser, et al., physica status solidi (a) 208, 1873 (2011).

4 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 4 Contents SEIRA with metal-particle layers SEIRS with metal nanowires Role of absorption and scattering Quantum effects

5 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 5 "SEIRA active" films, rule, examples Eloc E0! Dparticle + dgap AFM 500nm x 500nm, 48 nm mittlere Cu on CaF2(111) at 400 K, UHV growth dgap SEM image of a wet-chemically grown gold-island layer on an Si wafer, ca. 350 nm x 350 nm. A monolayer of APTES was used to improve gold nanoparticle adhesion. AFM 200nm x 200nm, 5nm Cu on MgO(001), UHV, 300K AFM 500nmx500nm, Ag grown on MgO(001) at 400K, UHV, ca. 26nm! AFM 500 nm 500 nm, silver films grown at 300K on MgO(001) in UHV, average film thickness: (a) 1nm Ag; (b) 3.4nm Ag; (c) 5.3 nm Ag AFM 500nm x 500nm, 3 nm Fe/ MgO(001), anealed, UHV growth

6 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 6 SEIRA with metal-particle films Transmittance of Cu on KBr(001) versus average Cu thickness (in nm). AFM, 500 nm x 500 nm, ca. 10nm Cu on CaF 2 grown at 300K, UHV SEIRA of condensed ethane (10 Langmuir exposure at 50 K) on Cu-island film on KBr. Regarding ice, signals are about 100 times bigger. The Cu layer is close to percolation. It was deposited at room temperature and corresponds to 8.4 nm average thickness. Reference is the bare island layer.

7 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 7 C2H6 layers on copper-island film at 50K gas: staggered "Surface" mode detected => C2H6 adsorbed in eclipsed configuration All other IR modes with frequencies close to those of the free molecule (van der Waals solid). A. Priebe, A. Pucci, W. Akemann, H. Grabhorn, A. Otto, J. of Raman spectroscopy 37, 1398 (2006). A. Priebe, A. Pucci, and A. Otto, J. of Physical Chemistry B 110, 1673 (2006) A. Pucci, physica status solidi (b) 242, 2704 (2005)

8 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 8 SEIRA lineshape and enhancement Maximum signal and asymmetry of SEIRA lines near percolation threshold! Decription with Bruggeman model works, scattering is not considered (small islands) percolation Calculation, 2D Bruggeman, one oscillator, filling factor F as parameter F ε ε metal eff = ( F 1) ε ε ads eff ε metal + ε eff ε ads + ε eff O. Krauth, J. Chem. Phys. 113 (2000) 6330 A. Priebe,et al., J. Chem, Phys. 119 (2003) 4887

9 calculation d = 3.0 nm F = 0.48 d = 4.5 nm F = 0.49 d = 6.1 nm F = 0.52 T=300K enumber [cm -1 ] relative transmittance experiment calculation d = 5.0 nm F = d = 3.0 nm F = 0.48 d = 4.5 nm F = 0.49 d = 6.1 nm F = 0.52 T=300K wavenumber [cm -1 ] relative transmittance experiment d = 5.0 nm F = 0.5 calculation d = 3.0 nm F = 0.48 d = 4.5 nm F = 0.49 d = 6.1 nm F = 0.52 T=300K wavenumber [cm -1 ] relative transmittance experiment calculation d = 5.0 nm F = d = 3.0 nm F = 0.48 d = 4.5 nm F = 0.49 d = 6.1 nm F = 0.52 T=300K wavenumber [cm -1 ] relative transmittance d = 5.0 nm F = wavenumber [cm -1 ] d = 3.0 nm F = 0.48 d = 4.5 nm F = 0.49 experiment calculation d = 6.1 nm F = 0.52 T=300K relative transmittance experiment calculation d = 5.0 nm F = d = 3.0 nm F = 0.48 d = 4.5 nm F = 0.49 d = 6.1 nm F = 0.52 T=300K wavenumber [cm -1 ] relative transmittance d = 5.0 nm F = wavenumber [cm -1 ] d = 3.0 nm F = 0.48 d = 4.5 nm F = 0.49 experiment calculation d = 6.1 nm F = 0.52 T=300K A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 9 SEIRA and Bruggeman simulation F ε ε metal eff = ( F 1) 1 ε eff ε metal + ε eff 1+ ε eff F ε ε metal eff = ( F 1) ε ε ads eff ε metal + ε eff ε ads + ε eff Relative IR transmittance spectra (circles) at normal incidence of Cu films grown at 300K. The MgO substrate was prepared by cleavage in UHV. The average metal thickness d. IR transmittance of about 6 L C 2 H 4 on KBr (green line) and on 6.1nm Cu/MgO (blue line) at normal incidence normalized to the transmittance of the pure film. The red line follows from the in-plane dielectric function for the metal-c 2 H 4 mixture and it is calculated with the 2D- Bruggeman model and a Lorentz-type dielectric function. A. Priebe, et al., J. Chem, Phys. 119 (2003) 4887

10 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 10 SEIRA and enhanced TO-phonon absorption of substrate rel. transmittance cm nm 0.76 nm 1.06 nm 1.26 nm 1.36 nm 1.46 nm 1.56 nm 1.66 nm 1.76 nm 1.86 nm 1.96 nm 2.06 nm 2.16 nm 2.27 nm 2.37 nm 2.47 nm 2.57 nm 2.67 nm 2.82 nm increasing Fe coverage rel. transmittance cm nm 1.21 nm 1.46 nm 1.62 nm 1.74 nm 1.86 nm 1.98 nm 2.09 nm 2.21 nm 2.33 nm 2.45 nm 2.57 nm 2.68 nm 2.80 nm 2.98 nm AFM 25 nm x 25 nm, 2 nm Fe on MgO(001), ca. 5 nm NP size Fe island films on 3 nm and 140 nm SiO 2 /Si, 300 K, UHV (reference is the wafer with oxide) Absorption (decreased transmittance) at the TO frequency of SiO 2 at 1070 cm -1 is enhanced due to metal islands while for thick continous layers absorption is screened. 3 nm SiO wavenumber [cm -1 ] 140 nm SiO wavenumber [cm -1 ]

11 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv Enhanced phonon signals with extended gold particles 11 Gold-island layer on an Si wafer with 3 nm nat. oxide, SEM ca. 350 nm x 350 nm, NP size ca. 100 nm

12 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 12 SEIRS with metal nanowires! SEM of a typical electron-lithographically produced gold antenna (on silicon wafer with natural oxide, 10 nm Ti adhesion layer between gold and silicon oxide. 40 nm gap AFM, PFT mode, gap region of a dimer on CaF2, IIT A non-ideal, grainy nature is visible.

13 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 13 Nanoantenna resonances Experimental extinction cross-section related to the geometrical one of gold nanoantennas with different lengths L on a CaF 2 substrate, normal incidence of light with an electrical field vector parallel to the long antenna axis. Resonance photon wavelength λ res as extracted from the spectra shown left. A linear relation λ res = 3.178[1/nm] L+ 451nm) gives a perfect fit to the data. D. Weber, et al., Opt. Mater. Express 1,1301 (2011)

14 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 14 Nanoantenna resonance preparation issues Single gold wire on CaF 2 - Heating steps IIT 2012, non-ideal, grainy nature Relative Transmittance Wavenumber (cm -1 ) before heating T = 200 C / t = 15min T = 200 C / t = 120min J. Vogt, Heidelberg 2012

15 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 15 Resonant nearfield - intensity enhancement length L 1µm ø 100 nm Calculation and figure by Aitzol Garcia-Etxarri At resonance, the nearfield intensity at the tips is at least by two to three orders of magnitude enhanced F. Neubrech et al., Phys. Rev. Lett. 101, (2008)

16 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 16 SEIRS of SAMs on singly-crystalline nanoantennas A. García-Etxarri Polarization dependent relative transmittance spectra of individual electro-chemically grown gold nanoantennas covered with a monolayer octadecanethiol ODT. Besides the broadband plasmonic response, narrow spectral features are found at 2855 and 2929 cm -1 which can be assigned to CH 2 stretching vibrations of ODT. Depending on the tuning ratio (as the frequency ratio of plasmonic resonance and the vibrational excitation, approximate numbers are given), differently looking vibrational signals appear on the plasmonic background. F. Neubrech et al., Phys. Rev. Lett. 101, (2008)

17 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 17 SEIRS: lineshape, enhancement < SEM, 200nm x 200 nm Baseline-corrected vibrational signals of the CH 2 and CH 3 vibrational modes of one monolayer of ODT for different measurement geometries as indicated in each panel. The IR reflection absorption spectroscopy (IRRAS), where a large area with ODT molecules contribute to the signal acts as reference signal for for SEIRS. In case of SEIRA, adsorbates on sidewalls of island on a cm 2 -sized sample area contribute to the signal. (D. Enders, A. Pucci, Appl. Phys. Lett. 2006) For SEIRS on gold nanowires, the signal strength as well as the line-shape strongly depends on tuning. The vibrational signal arises from the tip end of the nanowires where the nearfield is strongly enhanced. SEIRS spectra after baseline correction. F. Neubrech et al., Phys. Rev. Lett. 101, (2008)

18 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 18 SEIRS of SAMs, enhancement factor o electrochem. grown gold wires, GSI Darmstadt Enhancement factor in dependence on the tuning ratio between vibrational and plasmonic resonance (maximum of resonant extinction). Recent studies clarified that maximum enhancement is at the position of the near-field maximum that is slightly shifted from the far-field extinction maximum (P. Alonso-González et al.).

19 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 19 Fano effect ideal Vibrational excitation Plasmonic excitation SEIRA, SEIRS phenomenomlogical asymmetry parameter q as ratio of the transition probabilities (Fano 1961), ( ) ε = 2 E E 0 γ 0, E 0 resonant energy (narrow line), γ 0 width Schematics from A. E. Miroshnichenko et al., REVIEWS OF MODERN PHYSICS 82, 2257(2010).

20 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 20 Fano profiles, asymmetry parameter q anti-absorption, anti-resonance max. asymmetry Lorentzian absorption line phenomenomlogical asymmetry parameter q as ratio of the transition probabilities (Fano 1961), ( ) ε = 2 E E 0 γ 0, E 0 resonant energy (narrow line), γ 0 width

21 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 21 Role of coupling parameter SP Fano effect Rabi splitting Vacuum Rabi splitting with a single quantum dot in the center of a dimer nanoantenna. Left: Sketch of the system and of the excitation. Right: Calculated extinction cross sections as a function of the wavelength of the input field obtained for different dipole moments µ of the quantum dot. S. Savasta et al, ACS Nano, Oct. 2010

22 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 22 Coupling parameter g Simple analytical model with an opticaly active medium and a SP mode, both described as harmonic oscilators that have the same resonance frequency ω 0 (following S. Savasta et al, ACS Nano, Oct. 2010): g is the coupling rate. If the SP mode interacts with N quantum emitters (oscillators) that all experience the same SP field intensity, and that the coupling for one emitter is g 1, the resulting total coupling increases according to g= N g 1 with g 12 ~Γ 0 γ SP [ρ(r,ω 0 )-1], Γ 0 ~ Iµ 12 I 2 as spontaneous emission rate, ρ as enhancement of field mode density (intensity enhancement). Vacuum Rabi splitting between the two energies Re(Ω + ) and Re(Ω - ) appears when g 2 >(γ SP - γ 0 ) 2 /16. If the intrinsic value of γ 0 of the narrow transition is much smaller than γ SP, the criterion for strong coupling can be approximated by g >γ SP /4. For g <γ SP /4 coupling leads to a Fano line of the narrow oscilator on the SP background. Larger g lead to higher SEIRS. SEIRS is not simply linearly related to N and depends on the coherence of the narrow oscillation.

23 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 23 Role of width of narrow oscillator quantum emitter in the gap of a nanoparticle dimer. γ 0 γ 0 γ 0 γ 0 A. Manjavacas et al., Nano Lett Dependence of the optical absorption spectrum on the quantum emitter resonance width γ 0. The Fano resonance disappears as γ 0 increases. SEIRS: Adsorbed water layer invisible

24 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 24 Nanosensor principle In reality, functionalization and specific adsorption do not lead to well ordered layers! Coverage is not well known.

25 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 25 SEIRS of disordered layers Relative transmittance spectrum of gold nanoantennas (L= 1450nm, width and height 60nm, CaF 2 substrate) covered with a methylene blue monolayer. In the middle panel, a baseline-correction is obtained using a polynomial fit, whereas in the lower panel the second derivate is calculated. Both methods are suited to extract hardly visible transmission changes. From the two marked vibrational signals the one at 1736 cm -1 is not a mode of the free molecules. This mode arises upon adsorption on gold (or is a degradation effect). In our example the mode appears quite strong because it is close to the plasmonic resonance.

26 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 26 Surface enhanced IR spectra of GIPC1 Relative IR transmittance of gold nanoantenna arrays with various antenna length L, electric field parallel (par) and perpendicular (per), respectively to antenna. The antennas are covered with a GIPC1 layer prepared by selfassembling from a solution*. The molecules slightly modify the antenna resonance curves at the frequencies of the amide I and II bands ( broken lines). *Preparation by Polina Brangel, National Institute for Biotechnology in the Negev, Ben-Gurion University

27 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 27 Surface enhanced IR spectra of GIPC1 SEIRS spectra after baseline correction (with a linear baseline in the amide band s range, preliminary data). The enhancement is not maximum because of some detuning between antenna resonance and vibration frequencies. The Fano-type shape is clearly visible. Interestingly, the total line shape indicates dipolar interaction between the two amide bands.

28 F. Neubrech et al., Journal Phys. Chem. C 114, 7299 (2010) A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 28 SEIRS of substrate-surface phonon polaritons Relative transmittance spectra of nanoantennas (L as given) prepared on a Si wafer with a natural SiO 2 layer (thickness 3 nm). Reference is the bare wafer.

29 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 29 Fano-type line shape of phononpolariton excitation Baseline corrected transmittance spectra Frequency of SiO 2 signal: 1230cm -1 ( for maximum anti-absorption), not at ω TO =1065cm -1, which indicates the excitation of a polariton mode via scattering.

30 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 30 Comparison of enhanced phonon signals SEIRA signal with Fe islands Comparison of SiO 2 signal enhancement provided by individual antennas (red) and a dense Au-island films (black). From the relative transmittance, absorption was calculated and, for the black curve, a baseline correction was done.

31 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 31 Electromagnetic mechanism of surfaceenhanced light scattering P. Alonso-González et al., Nature Comm. Feb Spatial mapping of surface-enhanced light scattering. A Si tip (vertically oscillating at frequency Ω) is scanned across a Au rod antenna. Both antenna and tip are illuminated with s-polarized light. The s-polarized light backscattered from the tipantenna configuration is detected interferometrically (not shown). Demodulation of the detector signal at a higher harmonic nω yields the amplitude E n and the phase Δϕ n at each position of the tip. Topography, amplitude E n and phase shift Δϕ n maps of a Au rod antenna. The scale bar denotes 1 µm.

32 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 32 Experimental evidence: intensity elastically scattered scales with the fourth power of the local field enhancement P. Alonso-González et al., Nature Comm. Feb slope of 4.08 Left: Measured intensity I n E n 2 (red symbols) and calculated field enhancement f (black solid line) at the hot spot as a function of the antenna length L. Both quantities are normalized to their maximum value. The red solid line shows the function f 4.08 (L). Right: Parametric representation of log[i n (L)] and log[f(l)] (red symbols). A linear least-square fitting of the data points (red solid line) yields a slope of =>SEIRS enhancement 10 6 possible via scattering

33 J. Bochterle et al., ACS Nano, A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 33 Quantum effects below 1 nm CO ice on gold antenna Peak area of the vibrational signal of CO ice on gold and the shift of the plasmon resonance versus layer thickness (a). Ratio proportional to the signal enhancement induced by the antennas (b). signal enhancement

34 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 34 Summary: Plasmonic enhancement of IR vibrational signals due to electromagnetic field concentration near particles with plasmonic resonances or phonon-polariton resonances increase in absorption (SEIRA, average enhancement ca. 100 to 1000), vibrational signatures in light scattering (SEIRS) much higher enhancement up to SEIRA/SEIRS are Fano-type effects. Quantum effects below 1 nm from gold surface

35 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 35 Conclusions SEIRA SEIRS Maximizing vibrational signals: strong resonant scattering contribution, large coupling, and small damping/linewidth vibrating groups more than 1nm away from plasmonic surface => electromagnetic SEIRS as strong as electromagnetic SERS, but no flourescence background, no sample destruction

36 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 36 Acknowledgement San Sebastian- Donostia: J. Aizpurua, R. Hillenbrand Darmstadt: E. Toimil-Molares Tsukuba: T. Nagao, H.V. Chung Genova: E. Di Fabrizio Stuttgart: H. Giessen Paris: M. Lamy de la Chapelle Messina: P. G. Gucciardi KIP 2012 Andreas Otto

37 A. Pucci November 2012 Nanotwinning Project Meeting Kyiv 37 More on IR nanoantennas and SEIRS T. W. Cornelius, et al., Appl. Phys.Lett. 88, (2006). M. Klevenz, et al., Appl. Phys.Lett. 92, (2008). F. Neubrech et al., Phys. Rev. Lett. 101, (2008). F. Neubrech et al., Appl. Phys. Lett. 93, (2008). A. Pucci, et. al., Electromagnetic nanowire resonances for field-enhanced spectroscopy, in: One- Dimensional Nanostructures, Springer New York, 2008, pp F. Neubrech, et al., Properties of gold nanoantennas in the infrared, in: Nanostructures in Electronics and Photonics, World Scientific Publishing, 2008, pp H. V. Chung, et al., Proc. SPIE "Plasmonics:...", 7394 (2009), p E. F. Neubrech et al., Appl. Phys. Lett. 96, (2010). A. Pucci, et al., Phys. Stat. Sol. (B), 247, 2071 (2010). F. Neubrech et al., J. Phys. Chem. C 114, 7299 (2010). D. Weber et al., Optics Express, 19, (2011). G. Han et al., Nanotechnology 22, (2011). D. Weber, et al., Opt. Mater. Express 1,1301 (2011). F. Neubrech, et al., ACS Nano 6, 7326 (2012). F. Neubrech and A. Pucci, Surface enhanced infrared spectroscopy, in Nanoantenna, Pan Stanford Publishing, 2012, in press. D. Weber and A. Pucci, Antenna interaction in the infrared, in Nanoantenna, Pan Stanford Publishing, 2012, in press. J. Bochterle, F. Neubrech, T. Nagao, A. Pucci, ACS Nano 2012, accepted for publication.